I’m very curious as to why he wouldn’t want to stay at DAMS. They were easily the best team in GP2 this year.

However three scenarios come to mind that might explain why he will leave the team:

1) He doesn’t have much say in the matter. He may not have enough money to continue running in what is becoming a very expensive series, or the team may feel that he is not living up to expectations, particularly after Valsecchi won the title and he could only manage tenth (Calado, the highest-placed rookie, was fifth overall).
2) He thinks that joining another team will give him a better chance of making it to Formula 1. In this case, I would expect him to go to Lotus; Esteban Gutierrez has been links to a Sauber seat, whilst James Calado is believed to have run out of money.
3) He is leaving GP2 altogether, probably for Formula Renault 3.5, which is the better series these days. Although DAMS has a team there, Nasr would be better off trying to get into Tech 1, Arden Caterham or Fortec.

I was glad to see such a promising driver enter GP2 this year, and I’d be sad to see him leave for Formula Renault 3.5.
I remember Jean-Paul Driot saying he was happy with Nasr and that he’d likely be at DAMS in 2013, but I could be wrong.
I hope he remains at DAMS; if that isn’t the case I hope he changes team but not series.
Unless DAMS don’t want him, by leaving them he’s eyeing a stronger team, and I can only think of Lotus ART. Gutierrez could be off to F1 and honestly I don’t know whether he’d remain in GP2 if that wasn’t the case. They could keep Calado as they don’t strike me as a team who desperately needs cash, and probably the Brit can bring a few more sponsors after his great debut season. Nasr could be a perfect partner, as both would be young but with one season of experience. They could both battle for the title. And I’m pretty sure Nasr’s sponsors bring plenty of money, so Lotus are not going to be without money but, like this year, with little money from one driver and a lot from the other.